Nanopore membrane devices having pore size in the order of 1 nanometer in internal diameter have shown promise in rapid nucleotide sequencing. When a voltage potential is applied across the nanopore immersed in a conducting fluid, a small ion current due to conduction of ions across the nanopore can be observed. The size of the current is sensitive to the pore size. When a molecule such as a DNA or RNA molecule passes through the nanopore, it can partially or completely block the nanopore, causing a change in the magnitude of the current through the nanopore. It has been shown that the ionic current blockade can be correlated with the base pair sequence of the DNA molecule.
However, this technology still faces various challenges and so far it has not been able to discriminate down to a single base pair. In particular, the electrical potential needed to attract a ssDNA molecule in the nanopore tends to cause the ssDNA molecule to pass through the nanopore very quickly, making analysis difficult. To solve this problem, attempts have been made to tether the ssDNA to a bead to arrest the movement of the ssDNA molecule through the nanopore. However, such an approach may involve extensive sample preparation and may not be suitable for small sample sizes. Improved techniques for DNA analysis using nanopore membrane devices are needed.